Data may be transmitted as a sub-carrier in the lower vestigial sideband (VSB) spectral region of a standard television signal, e.g., a National Television Standards Committee (NTSC) broadcast video signal. Normally the standard television signal is generated by double sideband modulating a radio frequency (RF) picture carrier with a baseband composite video signal and thereafter vestigial filtering the modulated signal to remove the majority of the lower sideband. The vestigial sideband, which nominally extends to 1.25 MHz below the picture carrier, contains low frequency luminance information. This low frequency luminance information within the vestigial sideband is duplicated by low frequency luminance information within the television signal extending from the picture carrier to 1.25 MHz above the picture carrier. It has been determined that a portion of the luminance information in the vestigial sideband may be replaced with auxiliary digital audio information or other information without significantly affecting the video signal recovered by a receiver. The other information may comprise, e.g., a quadrature phase shift keying (QPSK) modulated data signal.
K. Jonnalagadda, in U.S. Pat. No. 5,029,003, discloses an apparatus for removing video signal from a portion of the vestigial sideband of a television signal and inserting a digital audio signal therein. Unfortunately, the disclosed apparatus is susceptible to the introduction of errors in the inserted digital audio signal due to video crosstalk.
Therefore, it is seen to be desirable to provide a video crosstalk resilient apparatus and method for inserting data as a sub-carrier in the lower VSB spectrum region of a television signal.